Photographic silver halide emulsions and developers containing 5-acyloxypyrazole color formers



Patented Nov. 13, 1951 PHOTOGRAPHIC SILVER HALIDE EMUL- SIONS ANDDEVELOPERS CONTAINING -ACYLOXYPYRAZOLE COLOR FORMERS Elmore LouisMartin, Wilmington, Dcl., assignor to E. I. du Pont de Nemours &Company, Wilmington, DeL, a corporation of Delaware No Drawing.Application August 21, 1946, Serial No. 692,143

8 Claims.

Thi invention relates to processes of color photography and to developersolutions and photographic emulsion layers therefor, utilizingfi-acyloxypyrazoles which have an unsubstituted hydrogen atom attachedto a carbon atom in the 4-position of the pyrazole ring.

Some 5-acyloxypyrazoles have been desscribed in the chemical literature.Various procedures for preparing them are referred to in Handbuch fiirOrganischen Chemie, Beilstein Prager- Jacobsen, vol. XXIV. Tw recentliterature articles disclosing such compounds are in the Journal of theAmerican Chemical Society, vol. 65, pages 1495 to 1502, and vol. 66,pages 1851 to 1855. The latter articles, while teaching the utility ofvarious other pyrazole derivatives for color coupling developmentprocesses of forming photographic dye images, imply that the 5-acyloxpyrazoles disclosed are unsuitable for such uses.

An object of thi invention is to provide processes of formingphotographic dye images utilizing 5-acyloxypyrazoles. A further objectis to provide processes for the color coupling development of silverhalide images utilizing S-acyloxypyrazoles which have an unsubstitutedhydrogen atom attached to the carbon atom in the 4-position of thepyrazole' ring. A further object is to provide practical methods ofincorporating such compounds int photographic developer solutions andwater-permeable colloid coating solutions. Still other objects will beapparent from the following description of the invention.

It has been established that photographic dye images can be produced bydeveloping exposed or reducible silver halide images in the presence -ofa 5-acyloxypyrazole having an unsubstituted hydrogen atom attached tothe carbon atom in the 4-position of the pyrazole ring. This may beaccomplished by incorporating the said compounds with a photographicdeveloper solution containing a primary, aromatic, amino, colordeveloping agent or by incorporating the said compounds in a hydrophiliccolloid-silver halide emulsion layer or in a hydrophilic colloid layerwhich is in operative contact with such an emulsion layer.

The 5-acyloxypyrazoles in question may be advantageously incorporatedwith the developer solutions by dissolving them in a water-miscible,organic solvent or a mixture of water and such a solvent and admixingthe resulting solution with the aqueous developer solution. Anotherpractical method consists of bringing the aforesaid compounds intoaqueous solution by means of a hydrotropic agent and admixing thesolution With the aqueous developer. Both the water-miscible organicsolvent and a hydrotropic agent can be used if desired.

Water-permeable colloid layers including those which containlight-sensitive silver halides can be made by admixing the aqueoussolution of the colloid with a solution containing the 5-acyloxypyrazolehaving an unsubstituted hydrogen atom attached to the carbon atom in the4-position of the pyrazole ring described in the preceding paragraph.Thus they may be added to a gelatinosilver halide emulsion which is thencoated onto a suitable support and dried.

In the case of the 5-acyloxypyrazoles which contain a solubilizing'group, e. g., a free carboxylic acid group or sulfonic acid group or awater-soluble salt thereof, e. g., alkali metal including sodium,potassium, ammonium, diethylamine, diethylcyclohexylamine, etc., it isnot necessary to use water-miscible solvents or hydrotropic agents.

The 1- and 3-positions of the 5-acyloxypyrazoles may be substituted byvarious groups or radicals which do not interfere with color couplingdevelopment reactions. Thus they may contain aryl, alkyl, aralkyl,cycloaliphatic or heterocyclic radicals which have one or more hydrogenatoms thereof substituted by various groups, e. g., halogen includingchlorine and bromine, sulfonic acid, carboxylic acid and theirwater-soluble salts, amide, nitro, alkoxy, aryloxy, etc.

A group of such 5-acyloxypyrazoles well-suited for use in thephotographic processes and compositions in question maybe represented bythe formula wherein Y is a member taken from the group consisting ofcarbonyl CO) and sulfonyl (-SO2.) radicals, Z-Y is an acyl radical, R isan aryl or substituted aryl radical or a heterocyclic radical joined tothe N atom of the pyrazole ring through a carbon atom, and R is amonovalent hydrocarbon nucleus or the same If it is desired to introduceselected substituents into the R. or R groups, this may be accomplishedprior to or after either of the steps by the normal chemicalmanipulations. v

In the formula Z-Y may be the acyl radical corresponding to a carboxylicacid or a sulfonic acid of the formula ZYOI-I. Thus Z-Y may be,

the acyl radical of an aliphatic, aliphatic-aromatic, cycloaliphatic,aliphatic, aromatic or heterocyclic carboxylic or sulfonic acid, e. g.formyl,

acetyl, methoxyacetyl, beta-carboxypropionyl, chloracetyl, carbethoxy,caproyl, stearoyl --OC--(CH2)1|.CHO

OCHz oo-(cm),.cnl

CH2 -OC(CH2) n-COOCH3, benzoyl, chlorobenzoyl,

nitrobenzoyl, toluenesulfonyl, butanesulfonyl, benzenesulfonyl,picolinoyl, nicotinoyl, isonicotinoyl, thienoyl, etc.

Suitable specific radicals for R include methyl, phenyl, naphthyl,carboxyphenyl, sulfophenyl, N substituted carbamylphenyl, N substitutedsulfamylphenyl, chlorophenyl, nitrophenyl, aminophenyl, pyridyl,benzothiazolyl, carboxymethoxyphenyl, beta-sulfoethyl,beta-carboxyethyl, sulfo 2 chloro-phenyl, propanol 2 sulfonic acid-3,etc.

Suitable additional specific radicals for R include methyl, phenyl,ethyl, furyl, naphthyl, carboxyphenyl, nitrophenyl, chlorophenyl,carbethoxymethyl, methoxyphenyl, benzyl, and isopropyl. The5-acy1oxypyrazole compounds set forth in copending applications SerialNumber 667,125, filed May 3, 1946, now U. 5. Patent No. 2,476,987, andSerial Number 682,137, filed July 8, 1946, now U. S. Patent No.2,476,988, including the various specific classes therein described areuseful in the present invention.

A convenient and practical method for the preparation ofS-acyloxypyrazoles comprises reacting a fi-pyrazolone having an activemethylene group in the 4-position with at least one molecular equivalentof an acyl halide and an acid binding agent, e. g., an inorganic basesuch as sodium hydroxide, potassium hydroxide, and sodium carbonate, oran organic base, e. g., pyridine, piperidine, diethylcyclohexylamine,ethylenediamine, diethylamine, etc.

The following examples illustrate in greater detail the invention. Theparts of reagents given in the examples are by weight. By the expression5-acyloxypyrazole nucleus is meant the pyrazole ring system remainingafter the removal of R and R in the general formula.

EXAMPLE I A suspension of five parts of1-(4-carboxyphenyl)-3-methyl-5-pyrazolone in ten parts of aceticanhydride containing a trace of sodium acetate is heated gently until ahomogeneous solution is obtained and then is refluxed gently for anadditional period of fifteen minutes. The acetic acid and excess aceticanhydride are removed by distillation under reduced pressure on a steambath. The 1- (l-carboxyphenyl) -3- methyl-S-pyrazolyl acetate formed'isdissolved in diethyl ether and three parts of thionyl chloride areadded. A vigorous reaction occurs and sulfur dioxide and hydrogenchloride are evolved. The mixture is refluxed for fifteen minutes duringwhich time the evolution of gases ceases. The ether is removed byevaporation and the resulting 1 (4-chloroformy1phenyl) -3-methyl 5pyrazolyl acetate is added to a mixture of three parts ofm-aminobenzaldehyde dimethyl acetal in a solution of three parts ofpotassium carbonate in thirty parts of water at 5 C. The mixture isshaken vigorously and after several minutes the m [p-(5-acetoxy-3-methyl1 pyrazolyD- benzamidolbenzaldehyde dimethyl acetal is separated andwashed first with water and then with ether. About one part of thereaction product is dissolved in 50 parts of alcohol and 50 parts of adeveloper solution of the following composition is added:

Developer solution Parts p-Aminodiethylaniline hydrochloride 2.0 Sodiumcarbonate, monohydrate 20.0 Sodium sulfite, anhydrous 2.0 Potassiumbromide 0.5 Water to make 1000.0

A piece of film bearing a silver ferrocyanide image in a gelatin layeris developed in this photographic developer and after removal of themetallic silver by means of a bleach containing potassium ferricyanideand removal of the resulting ferrocyanide with sodium thiosulfate yieldsa clear, strong magenta dye image.

Development of a piece of film bearing a silver ferrocyanid-e image in agelatin layer with a photographic developer comprising two parts of theabove 1 (4 carboxyphenyl) 3 methyl- 5-pyrazolyl acetate and the abovedeveloper solution yields a clear, strong magenta dye image which isleached to a considerable extent by water due to the presence of thesolubilizing carboxylic acid group.

EXAMPLE II Development of a piece of film bearing a silver .ferrocyanideimage in a gelatin layer with a photographic developer comprising1-phenyl-3- methyl-E-pyrazolyl methyl carbonate (see Himmelbauer, J. pr.(2) 54, 189 (1896)) and p-a-minodiethylaniline as described in Example Igives a strong magenta dye image after removal of the silver image.

EXAMPLE III Development of a piece of film bearing a silver ferrocyanideimage in a gelatin layer with a solution ofN-B-(5-methylcarbonato-3-methyl-l-pyrazolyl) phenyl methyl urethane,

Development of a piece of film bearing a silver ferrocyanide image in agelatin layer with a solution of m [p ethylcarbonato-3-methyl-1-pyrazolyl) benzamidol benzaldehyde ethylene gly-. col acetal (seeExample II of application Serial Number 667,125, filed May 3, 1945, forproperties and preparation) in a p-aminodiethylaniline developer asdescribed in Example I gives a strong magenta dye image having a maximumabsorption of light of wavelength 535 m EXAMi EE v Development of apiece of film bearing a silver ferrocyanide image in a gelatin layerwith a solution of m-[p-(5-benzoxy-3-methyl1-pyrazoly1)phenoxyacetamido] benzaldehyde ethylene glycol acetal (see Example IIIof application Serial Number 667,125, filed May 3, 1946, for preparationand properties) with p-aminodiethylaniline developer as described inExample I gives a strong magenta dye image.

EXAMPLE VI To ten parts of a polyvinyl acetal having a 5-ethyl-carbonatopyrazole nuclei content of approximately six per cent andprepared as described in Example VI of application Serial Number682,137, filed July 8, 1946, now U. S. Patent No. 2,476,988, is added 60parts of alcohol, 135 parts of water, and 0.8 part of potassiumhydroxide solution. Solution is effected by warming to 70 C. for tenminutes with stirring. The essentially colorless 5% solution of thepolyvinyl acetal is cooled to 40 C. and is used to prepare an emulsionunder conditions which will not expose or cause fogging of the sensitivesilver salt as follows: To 90 parts of the 5% magenta colorformingpolyvinyl acetal solution is added 31 parts of 3 N ammonium bromide andtwo parts of 0.5 N potassium iodide. This solution is stirred at 50 C.while adding a solution of 29 parts of 3 N silver nitrate, 50 parts ofwater, and 15.3 parts of 28% ammonium hydroxide during one minute. Afterstirring for a total of one-half hour, 50-100 parts of a sodium sulfatesolution is added. The precipitated silver halide/color-formeremulsionis washed for one hour in running water, after which the excess water isdrained off. The remainder of the original solution, together with 35parts of ethanol and 15 parts of water, is added and the mixture isstirred at 65 C. for one-half hour. After cooling to C., the emulsion iscoated on a baryta sized white paper. The 'resulting paper is exposed toform a latent image, then developed in the developer solution given inExample I. The paper is then fixed in 25% sodium thiosulfate solution,Washed, bleached with 4% potassium ferricyanide, washedand fixed in 25%sodium thiosulfate. The resulting paper contains a bright, strongmagenta dye image.

EXAMPLE VII A 5% solution is prepared from ten parts of a polyvinylacetal containing 5-benzoxypyrazole nuclei prepared as described inExample V of application Serial Number 682,137, filed July 8'," 1946,now U. S. Patent No. 2,476,988, according to the procedure given inExample VI. Preparation of a silver halide emulsion containing such anacetal, coating on paper, and processing as described in Example IIIgives a strong magenta dye image.

6 EXAMPLE VIII Development of a piece of film bearing a silverferrocyanideimage in a gelatin layer with a photographic developercomprising two parts of 1-(4-carboxyphenyl) -3-methyl 5 pyrazolylptoluenesulfonate and the developer described in Example I yields aclear, strong magenta dye image which is leached to a considerableextent by water due to the presence of the solubilizing carboxylic acidgroup. The 1-(4-carboxyphenyl) 3-methyl-5-pyrazolyl p-toluenesulfonateis prepared as follows: To a solution of 160 parts of potassiumhydroxide in a mixture of 800 parts of water and 50 parts of dioxane isadded 218 parts of 1-(4-carboxyphenyl)-3-methyl-5- pyrazolone. Theresulting solution is cooled to 20 C. by means of external cooling andthen to 5 C. by the addition of crushed ice directly to the reactionmixture. A solution of 225 parts of p-toluenesulfonyl chloride in 225parts of anhydrous dioxane is added in one portion to the vigorouslystirred solution. After being stirred at 23 C. for one hour, thesolution is heated to 35 C. and acidified by the addition of 150 partsof 50% acetic acid. The crystalline product is collected, washedthoroughly with cold water and dried. I Crystallization of the dryproduct (five parts ethanol for each part of product) gives glistening,colorless needles melting at l85-187 C. in 80-90% yield. Analysiscalculated for C18H16O5N2S:C=58.03;H=4.33; S=8.61. Found: 0:57.04,51.31; H=4.71, 4.44; and S=8.31, 8.30.

EXAMPLE IX To a solution of 17 parts of 1-phenyl-3-methyl 5-pyrazolonein parts of pyridine cooled to 10 C. is added 15 parts of dichloroacetylchloride, the temperature being maintained at 10 C. by external coolingand by controlling the rate of addition of the acid chloride. Theresulting mixture is stirred for one hour at 10 C. and then for one halfhour at 20 C. Chloroform is added to the mixture and the resultingmixture extracted first with water, then with dilute hydrochloric acid,then 5% sodium carbonate solution, and finally with water. Concentrationof the chloroform layer yields an oil which cannot be induced tocrystallize. Treatment of an alcoholic alkaline solution of the oil inthe presence of p-aminodiethylaniline with aqueous potassium ferrocy-fanide gives a strong magenta dye. V

The ,5-acyloxypyrazoles may be incorporated into, the developer solutionor may be incorporated into the photographic layer or a layer coactivetherewith. The binding agent for the photographic layer may be gelatinor other colloidal material, such as collodion, partially hydrolyzedcellulose acetate, polyvinyl alcohol and its partially substitutedesters and acetals, hydrolyzed vinyl ester/olefin interpolymers,hydrophilic polyamides, etc. The carrier for the photographic layer maybe a transparent medium, such as glass, or a plastic material, e. g.,cellulose derivative or synthetic resin or superpolymer, e. g.,cellulose ester, polyvinyl acetals, polyamide, copolymers of selectedfluorine substituted ethylenes, etc., or a non-transparent reflectingmedium, such as paper or pigmented cellulose ester film. The5-acyloxypyrazoles may be used with single layer coatings or may be usedwith a plurality of layers which may or may not contain othercolor-forming dye compounds.

Various dispersing agents may be used for incorporating the5-acyloxypyrazoles into the photographic layer. Suitable such agentsinclude long chain alkyl sulfates and sulfonates, e. g., sodium dodecylsulfate and sodium chlorocetanesulfonate, non-ionic agents, e. g.,mannitan monopalmitate and ethylene oxide/alkylated phenol condensates,the betaines, such as C-cetylbetaine, cation-active agents, such ascetyl pyridinium bromide, and the soaps.

In the case of multilayer photographic film or paper in which the-acyloxypyrazole is incorporated into one or more layers, it may benecessary to use special precautions to prevent wandering of the5-acyloxypyrazoles from the sensitive layer in which it is incorporated.This may be accomplished by the use of 5-acyloxypyrazoles of polymericnature, such as the products described in copending applications SerialNumbers 624,587, now Patent No. 2,567,750, and 682,137, now U. S. PatentNo. 2,476,988, by the use of 5-acyloxypyrazoles which contain long sidechains, such as l- (3-stearamidophenyl) -3-methyl-5-pyrazolyl ethylcarbonate, l-phenyl- -stearyl-5-pyrazolyl ethyl carbonate, by the use of5-acyloxypyrazoles which are relatively insoluble in the photographicprocessing solutions.

Certain of the aldehydes containing 5-acyloxypyrazole groups describedin copending application Serial Number 667,125, now U. S. Patent No.2,476,987, are non-diffusing. Acid chlorides containingfi-acyloxypyrazole groups as described in application Serial Number657,629, filed March 27, 1946, now U. S. Patent No. 2,476,986, may beused to prepare products which are fast to diffusion as, for example, byreaction with high molecular weight amines, such as benzidine,p,pdiaminodiphenyl ether, etc., or by reaction with polymeric materials,such as gelatin, polyvinyl alcohol and its partially substituted estersand acetals, partially hydrolyzed cellulose esters, hydrolyzed vinylester-olefin-interpolymers, etc.

The acyloxypyrazoles may also be immobilized through suitable choice ofthe aoylating reagent. Thus, 1-phenyl-3methyl-5pyrazolone may be treatedwith long chain or polymeric acid chlorides or anhydrides, e. g.,stearoyl chloride, dodecoyl chloride, polymethacrylyl chloride andmaleic anhydride interpolymers with, for example, styrene and vinylchloride. This type of immobilization is of considerable interest sincethe final color-developed film can be treated with hydrolytic agents,such as dilute caustic, leading to removal of the uncoupled colorformers.

It is also possible to prepare 5acyloxypyrazoles containing twopyrazolone nuclei coupled through the acyloxy radicals, e. g., bytreatment of two moles of 1-phenyl-3-methyl-5-pyrazolone with one moleof a diacid chloride, such as adipyl chloride. Similarly by treatment ofa 5-pyrazclone with a dibasic acid anhydride, a 5-acyloxypyrazolonecontaining an acid group is formed, for example, maleic anhydride and1-phenyl-3- methyl-5-pyrazolone gives In place of the specific aromaticamino de veloping agent described in the examples, there may besubstituted various other specific agents of this type. These agentshave an unsubstituted amino group which apparently enables the oxidationproduct to. couple with the5-acyloxypyrazoles. Such agents include themono-, di-, and tri-amino aryl compounds and compounds formed therefromby substitution in the amino groups as well as in the ring. Thepreferred developing agents in the process of dye coupling developmentare derivatives of p-phenylenediamine, and particularly the asymmetricdi-N-substituted pphenylenediamines, for example,p-amino-dimethylaniline, 2 amino-5-diethylaminotoluene, etc. Thesearomatic amino developing agents may be used in the form of their saltswhich may be organic or inorganic. The salts are, in general, morestable than the free bases. As examples of suitable salts there might bementioned the hydrochloride, sulfate, oxalate, etc.

The photographic layers and emulsions may also contain the usualsensitizers, such as the cyanine and carbocyanine salts and bases andthe cyazines and carbocyazine salts and bases, em ployed to extend thesensitivity of the photographic emulsions.

The coupler compositions of this invention may also be used in thepreparation of positive dye images by developing an exposed silverhalide emulsion with a non-coupling developer, then sitposing to light,and developing with a coupling aromatic amino developer, that is, by acolor reversal process. Removal of the metallic silver by conventionalmethods yields a positive dye image.

A major advantage of the 5-acyloxypyrazole color formers is that theyyield more stable compositions than the corresponding S-pyrazolones fromwhich they are derived. Problems associ ated with the reactivity of theB-pyrazolones, for example, self-condensation to colored productsleading to stained films, are thus avoided or minimize. Because of thisstability, it is also possible to prepare complex color formerscontaining groups which would be impractical with the 5-pyrazolones, e.g., aldehyde groups. In addition, the 5-acyloxypyrazoles are moreresistant to oxidation than the B-pyrazolones. The acyl group can alsobe used to introduce substituents of a special nature, e. g.,solubilizing or immobilizing groups, which are later eliminated from themolecule as indicated above.

The exact mechanism by which these new color formers function to producedye images is not known with certainty. It is surprising that any coloris produced since there is no active methylene group in the5-acyloxypyrazoles. It appears probable that coupling takes place withsimultaneous or prior elimination of the acyl group. The relative easeof color coupling varies to some extent with the nature of the acylgroup as might be expected. Thus, the sulfonates are slowest to coupleand in some cases it is desirable to subject them to a hydrolytic stepprior to coupling in order to achieve high color densities. Manyphotographic emulsions are prepared under alkaline conditions favorableto the hydrolysis of compounds of this type and, although it has notbeen established, it is possible that hydrolysis of the5-acyloxypyrazoles may take place to some extent. If such a hydrolysisdoes take place, the acid liberated would be neutralized by the alkalipresent.

As many widely different embodiments of this invention can be madewithout departing from the spirit and scope thereof, it is to beunderstood that the invention is not to be limited except as defined bythe claims.

What is claimed is:

1. A colloid silver halide emulsion havingadded thereto a color formerhaving the general formula methyl, ethyl, isopropyl, phenyl,carboxyphenyl,

nitrophenyl, methoxyphenyl, chlorphenyl, benzyl and carbethoxy methyl,and R is a radical taken from the group consisting of methyl,propanol-2- sulfonic acid-3, p-sulfoethyl, fl-carboxyethyl, phenyl,carboxyphenyl, sulfophenyl chlorophenyl, nitrophenyl, aminophenyl,N-substituted carbamylphenyl, N-substituted sulfamylphenyl,CHsOOCNHCsH4-, carboxymethoxyphenyl pyridyl, and benzthiazolyl, and ZYis an acyl radical.

2. A photographic element hearing at least one hydrophilic colloidsilver halide emulsion layer having added thereto a color former havingthe general formula HC-G-R 4 a ZYC5 2N wherein Y is a member taken fromthe class consisting of carbonyl and sulfonyl radicals, R is a radicaltaken from the group consisting of methyl, ethyl, isopropyl, phenyl,carboxyphenyl, nitrophenyl, methoxyphenyl, chlorphenyl, benzyl andcarbethoxy methyl, and R is a radical taken from the group consisting ofmethyl, propanol-2- sulfonic acid-3, ,B-sulfoethyl, p-carboxyethyl,phenyl, carboxyphenyl, sulfophenyl, chlorophenyl, nitrophenyl,aminophenyl, N-substituted carbamylphenyl, N-substituted sulfamylphenyl,CI-bOOCNHCsH4-, carboxymethoxyphenyl pyridyl, and benzthiazolyl, andZ-Y- is an acyl radical.

3. A photographic developer composition comprising a weak alkali, aprimary, aromatic, amino developing agent and an added color formerhaving the general formula wherein Y is a member taken from the classconsisting of carbonyl and sulfonyl radicals, R is a. radical taken fromthe group consisting of methyl, ethyl, isopropyl, phenyl, carboxyphenyl,nitrophenyl, methoxyphenyl, chlorphenyl, benzyl and carbethoxy methyl,and R is a radical taken from the group consisting of methyl,propanol-2- sulfom'c acid-3, fl-sulfoethyl, p-carboxyethyl, phenyl,carboxyphenyl, sul-fophenyl, chlorophenyl, nitrophenyl, aminophenyl,N-substituted carbamylphenyl, N-substituted sulfamylphenyl,CH3OOCNHCsH4-, carboxymethoxyphenyl pyridyl, and benzthiazolyl, and ZYis an acyl radical.

4. A photographic element bearing at least one hydrophilic colloidsilver halide emulsion layer having added thereto a color former of theformula is an acyl radical and Ar is an aryl radical.

5. A photographic element bearing at least one hydrophilic colloidsilver halide emulsion layer having added thereto a color former of theformula wherein wherein R' is an alkyl radical of 1 to 2 carbon atomsand Ar is an aryl radical.

6. A photographic element bearing at least one hydrophilic colloidsilver halide emulsion layer having added thereto a color former of theformula H300 0 0- 0- (J-CH:

7. A photographic element hearing at least one hydrophilic colloidsilver halide emulsion layer having added thereto a color former of (theformula o- -HNC o- N- N OHz-O I H5o2o0o-o-o C-CH;

on 8. A photographic element bearing at least one hydrophilic colloidsilver halide emulsion layer having added thereto a polyvinyl acetalcolor former which contains recurring units of the formula CH2 C HNO 0-NN (m-(f l H (g HsCzOOC-O-C C--CH3 ELMORE LOUIS MARTIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Weissberger, Investigation ofPyrazole Compounds IV, etc., J. A. C. S. 65, pages 1495 to 1502 (1943),all cited.

Weissberger, Investigation of Pyrazole Compounds VII, etc., J. A. C. S.66, pages 1851 to 1855 (1944 all cited.

1. A COLLOID SILVER HALIDE EMULSION HAVING ADDED THERETO A COLOR FORMERHAVING THE GENREAL FORMULA